Detecting Memory Leaks

This article was contributed by Stefan Soltsien.

This article describes how to get the callstack for memory leaks in a certain component (EXE or DLL) of your Visual C++ program. The code provided with this article works on WindowsNT. It should work on Windows9x systems as well, although it has not been tested on such systems. There is another restriction, that it only works on Intel x86 machines. It has been written with MS Visual C/C++ 5.0, but it should work fine with Version 6 of the Developer Studio as well. The example program is written with the Active Template Library (ATL), but it does not contain any COM stuff.

Usage

To detect memory leaks in the components of your application, you just have to add the following lines anywhere to the code of your component:

	#include "c:\temp\HookAlloc\MemoryTracking.h"
	USE_MEMORYTRACKING("c:\\temp\\allocations.log",true)
	#pragma warning(disable:4073)							
	#pragma init_seg(lib)

• the path in the #include-statement has to be adapted to your needs
• The Macro USE_MEMORYTRACKING("c:\\temp\\allocations.log", bLogAtStartup) defines the name of the Logfile (if NULL, all output is written to the debug output window) and specifies, whether logging is on or off at program startup
• To control the parts of your program where logging is on / off use the macros LOGGING_ON / LOGGING_OFF or BEGIN_NO_LOG_BLOCK / END_NO_LOG_BLOCK to switch off logging for a special part of code within a single function/method.
• The pragma you see above switches off the stupid compiler warning that an 'initializer has been put in "lib" initialisation area'. This warning is not needed at all, since we know what we are doing with the next line: MemoryTracking is set up before any of the "users objects" (like MFC's CWinApp derived object) are initialized.

Then:

• recompile your component (rebuild is NOT neccessary)
• start your program, and invoke those parts of it, where the leaks occur
• terminate the program and you'll get a list of memory leaks in your debug window of VC++
• open the log file, that has been defined with the macro USE_MEMORYTRACKING (see above) or take a look into the VC++ debug output window, depending if you have defined a log filename or not
• compare the numbers enclosed in curly braces (i.e. {1234} with the 'request'-numbers in the log file (or in the debug output window)

By looking at the call stack in the logfile, you may figure out which function or method has allocated the leak.

Tip:

If MFC is used, you may add the line '#define new DEBUG_NEW' to the cpp files of the project. Thus you provide information about where allocations occur to the new operator. For allocations (leaks) that have been made with DEBUG_NEW defined you can simply double-click the line preceeding the call stack of a leak description (in the debug output window) to jump to the appropriate position in the source code.

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